1. Field of the Invention
The present invention relates to an electromagnetic clutch and a method of the manufacture thereof and, more particularly, but not restrictively, to an electromagnetic clutch for use in an air conditioner for an automobile and to a method of manufacturing the electromagnetic clutch.
2. Description of the Prior Art
An electromagnetic clutch includes driving and driven rotary members or so-called "rotor discs" which are electromagnetically coupled together or uncoupled from each other. The prior art disc of a first type is formed of an annular material punched out from a sheet of steel. The disc includes radially sectionalized first, second and third zones or sections disposed in concentric relationship with each other and radially sectionalized or separated by outer and inner circular rows of openings. The openings in each row are circumferentially spaced to leave in the disc four radial bridges which mechanically interconnect the radially adjacent pair of sectionalized zones.
With the prior art rotor disc of the type referred to above, the magnetic flux passes also through the ineffective bridges with a resultant decrease in the effective flux. For this reason, the prior art electromagnetic clutch which incorporates the rotor discs of the type discussed must be of a large or bulky size.
A second type of the prior art rotor disc is formed of concentric and radially spaced first and second annular members both of a magnetizable material having radially opposed peripheral surfaces in which grooves are formed. The first and second annular magnetizable members are mechanically bonded together by three circumferentially spaced bond members of a non-magnetizable metal swaged into the annular space defined between the first and second magnetizable members. Each of the bond members when swaged is pressed in the axial direction of the disc to cause a plastic deformation so that the material of the bond member flows into the grooves. This bonding method, however, fails to provide adequate mechanical strengths and a mechanical stability for the reason to be discussed later.
As such, the first and second types of the prior art discs are not satisfactory in the view points of leakage flux and mechanical strengths.
U.S. Pat. No. 2,038,124 issued Apr. 21, 1936 to John L. Osborne teaches a method of mechanically connecting two radially spaced and concentric members by means of an insert or mechanical bond member swaged into the annular space defined between the two concentric members. U.S. Pat. No. 2,804,679 issued Sept. 3, 1957 to Ward D. Tracy and U.S. Pat. No. 3,559,946 issued Feb. 2, 1971 to David W. Baxter, Jr. contain similar teachings. These three U.S. Patents, however, are not concerned with electromagnetic clutches.